1. Field of the Invention
The present general inventive concept relates to an inkjet printhead, and more particularly, to a thermal inkjet printhead to enhance ink ejection characteristics thereof by preventing and/or dissipating heat accumulation around a heater thereof.
2. Description of the Related Art
An inkjet printhead ejects ink droplets on desired positions of recording paper in order to print predetermined color images. Inkjet printers are classified into two categories: a shuttle type inkjet printer having a printhead that is shuttled in a direction perpendicular to a transporting direction of a print medium, and a line printing type inkjet printer having a page-wide array printhead corresponding to a width of a print medium. The latter has been developed for realizing high-speed printing. The array printhead has a plurality of inkjet printheads arranged in a predetermined configuration. In the line printing type inkjet printer, during printing, the array printhead is fixed and a print medium is transported, thereby allowing the high-speed printing.
The inkjet printhead is categorized into two types according to the ink droplet ejection mechanism thereof: a thermal inkjet printhead and a piezoelectric inkjet printhead. The thermal inkjet printhead ejects ink droplets due to an expansion force of ink bubbles generated by thermal energy. The piezoelectric inkjet printhead ejects ink droplets by a pressure applied to ink due to a deformation of a piezoelectric body.
The ink droplet ejection mechanism of the thermal inkjet printhead is as follows. When a current flows through a heater made of a heating resistor, the heater is heated and ink near the heater in an ink chamber is instantaneously heated up to about 300° C. Accordingly, ink bubbles are generated by ink evaporation and the generated bubbles are expanded to exert a pressure on the ink filled in the ink chamber. Thereafter, an ink droplet is ejected through a nozzle out of the ink chamber.
FIG. 1 is a schematic cross-sectional view illustrating a conventional thermal inkjet printhead. Referring to FIG. 1, the conventional inkjet printhead includes a substrate 11 on which a plurality of material layers are stacked, a chamber layer 20 stacked on the substrate 11 and defining an ink chamber 22, and a nozzle layer 30 stacked on the chamber layer 20. Ink is filled in the ink chamber 22 and a heater 13 to heat the ink to generate bubbles therein is installed under the ink chamber 22. In addition, the nozzle layer 30 has a nozzle 32 to eject the ink.
The substrate 11 is generally a silicon substrate. An insulation layer 12 to provide insulation between the heater 13 and the substrate 11 is formed on the substrate 11. The insulation layer 12 is generally made of silicon oxide. The heater 13 to heat the ink in the ink chamber 22 to generate bubbles therein is disposed on the insulation layer 12. Conductors 14 to supply an electric current to the heater 13 are disposed on the heater 13.
A passivation layer 15 is formed on the heater 13 and the conductors 14 to protect the heater 13 and the conductors 14. The passivation layer 15 prevents the heater 13 and the conductors 14 from oxidizing or directly contacting the ink, and is generally formed of silicon oxide or silicon nitride. An anti-cavitation layer 16 is formed on the passivation layer 15. The anti-cavitation layer 16 protects the heater 13 from a cavitation pressure induced by bubble extinction, and is generally made of tantalum (Ta).
In this structure, some heat generated by the heater 13 is used to form bubbles and the rest of the heat (i.e., residual heat) should be dissipated through the insulation layer 12 formed under the heater 13 toward the substrate 11. However, because the insulation layer 12 is made of silicon oxide having low thermal conductivity, the residual heat generated by the heater 13 may not be dissipated toward the substrate 11, but instead may be accumulated in the insulation layer 12 near the heater 13. When the heat is accumulated in the insulation layer 12, the temperature of the ink filled in the ink chamber 22 increases, and thus a viscosity of the ink decreases, thereby degrading ink ejection characteristics, such as ink ejection frequency and ink ejection velocity.
Recently, line printing type inkjet printers have been actively developed to satisfy demands of high integration and high speed. Since an array printhead used in the line printing type inkjet printer includes many heaters, a large quantity of heat is generated from the heaters. Accordingly, if the conventional thermal inkjet printhead is employed in the array printhead, ink ejection characteristics thereof may degrade.